The present invention relates to a manual transmission unit for use in a vehicle, and more particularly to an improvement in the manual transmission units possessing synchronizers and at least one unsynchronized gear, such as reverse.
A widely known manual transmission has input and output shafts supported in a parallel relationship to each other within a housing assembly for the unit, an idler shaft supported in a parallel relationship with the shafts from the housing assembly, driving and driven gears respectively mounted on the input and output shafts, an idler gear which is axially slidable on the idler shaft, a folk shaft which is slidably supported in a parallel relationship with the idler shaft from the housing assembly and is operatively connected to a manual shift lever which is selectively shifted from its neutral position to a forward or reverse position, a detent mechanism mounted on the housing assembly for selectively rataining the fork shaft in its neutral and shifted positions under a resilient load acting thereon, a shift head member which is slidable on the fork shaft, a one-way engagement mechanism for effecting the engagement of the shift head member with the fork shaft through the axial movement of the fork shaft toward and away from its reverse position, and a shift arm member pivoted to the inner wall structure of the housing assembly and linked with the shift head member, wherein the idler gear is carried by the shift arm member to be retained in its neutral position and to be engaged with the driving and driven gears through axial movement of the fork shaft to its reverse position.
The reverse gear is usually constructed so that it is unsynchronized. Therefore, even after the vehicle comes to a complete stop, the input shaft, which runs into the transmission, is still rotating because of inertia. Hence, if an operator shifts into reverse while the input shaft is still rotating, a grinding noise may originate in the transmission resulting from the engagement between a rotating reverse drive gear, which is connected to the input shaft, and a stationary reverse idler gear. This results in discomfort to the operator and undesired wear on the gears.